The present invention relates to a spring-constant variable type stabilizer device which is disposed between left and right wheels of a vehicle.
As is known, a stabilizer mechanism in a suspension system of a vehicle is designed so that opposite ends of a stabilizer are secured to a lower arm through a link rod, and an intermediate portion thereof is rotatably supported on the vehicle body whereby where the left and right wheels of the vehicle are moved up and down in the same phase, a spring action caused by the stabilizer does not occur whilst where the upward and downward movement of the left and right wheels is in the reverse phase, a constant spring force is caused with a central portion of the stabilizer as a torsion bar. At the upward and downward movement of the left and right wheels in the reverse phase, the spring force of the stabilizer is made to act so that a fixed spring force may act with a central portion of the stabilizer as a torsion bar and at the time of upward and downward movement of the left and right wheel in the reverse phase, a phase difference thereof may be corrected thus increasing the rigidity with respect to the roll of the wheels and improve the running stability of the vehicle.
However, if the roll rigidity is reinforced by the stabilizer mechanism, the vibration of the vehicle on the spring increases as the total spring constant of the suspension system increases, and when the vehicle runs on the wavy road surface such that the left and right wheels of the vehicle take the upward and downward movement in the reverse phase, the comfortableness to ride becomes worsened.
In view of the foregoing, as one means for preventing the worsening of the comfortableness to ride, there have been developed a roll control system for the vehicle disclosed, for example, in U.S. Pat. Nos. 2,802,674 and 4,206,935 Specifications.
According to the systems disclosed in said patents, a control cylinder is arranged on the end of a stabilizer whereby when the control cylinder is in an expansible state, a torsional torque of the stabilizer is not transmitted to a lower arm, as a consequence of which when the vehicle runs on the wavy road surface, the vibration of the vehicle on the spring is increased to prevent the worsening of comfortableness to ride on the vehicle.
On the other hand, when the control cylinder is in a locked state to cease the expansion, the torsional torque of the stabilizer is transmitted to the lower arm to effectively prevent the roll of the vehicle during the running of the vehicle on the flat road.
However, in the aforementioned roll control system, the locked state of the control cylinder is not always produced at a neutral position but sometimes the piston stops at a position other than the neutral position. As the result, when the control cylinder is locked, the upper end thereof may not always be maintained at a constant level to bring forth a level difference between the left and right sides of the body, resulting in inconveniences such that the attitude of the vehicle becomes unstable and the running stability may not be secured.